This is a proposal for a new research project to study the mechanochemistry of a new type of mitochondrial coupling factor (F1) during ATP synthesis in beef-heart mitochondria. It is based on a recent finding by our laboratory that a new form of homogeneous F1 can be isolated by mild treatments, with properties more similar to the membrane-bound enzyme (subunit composition, sensitivity to aurovertin, adenine-nucleotide interconversion, latency of ATPase activity) than the conventional forms of F1. We propose to 1) characterize the kinetic parameters of the ATPase function of the new F1 and compare them to those of conventional F1, in order to understand the role of the subunit (the ATPase inhibitor subunit) found in stoichiometric amounts in the new F1; 2) analyze the conditions that can induce allomorphic interconversions in the new F1 preparations with the aim of understanding the mechanism(s) that regulate the conformational changes of this enzyme during ATP synthesis; 3) optimize the conditions for ADP transphosphorylation by the new F1 (it catalyzes this reaction while the conventional F1 does not) and characterize it as a model reaction for ATP synthesis.